The invention relates to drawing dies and measuring devices. Although devices are known which measure wall thickness and eccentricity, usually by means of ultrasound transducers, such devices generally rely on direct contact with the inner or outer wall of the tube and in many instances require that the tube be immersed in a bath of clean fluid, usually water. The aforementioned class of devices are typically slow moving inspection type devices to which the tube is subjected after it is formed. Such devices merely permit one to tell, after the fact, whether a tube has been made properly. Thus, it is quite possible that a large quantity of inferior product can be produced before there is any knowledge of such fact. Obviously, it would be more desirable to know the instant a tube is being drawn whether it is satisfactory so that corrections can be made to improve the tube produced later or to facilitate the segregation of various lengths or coils of tubing in accordance with their minimum wall thickness, for example. Generally, a given end use for a tube will require a certain minimum wall thickness. Thus, it is obvious that if one can produce tubing whose minimum wall thickness is known to be very close to the average wall thickness, i.e., has very little eccentricity, such tubing will require less metal per unit of length and will cost less to produce. In U.S. Pat. No. 2,213,983, an apparatus for measuring the thickness of a cast metal sheath around a cable is disclosed but such apparatus would have little or no usefulness in connection with a present day tube drawing operation wherein drawing speeds of 1000 feet per minute or more are common.